/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import java.util.Collections;
import java.util.Map;
import java.util.Set;

/**
 * A base implementation of {@link NetworkConnections} for undirected networks.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
abstract class AbstractUndirectedNetworkConnections<N, E> implements NetworkConnections<N, E> {
    /** Keys are edges incident to the origin node, values are the node at the other end. */
    protected final Map<E, N> incidentEdgeMap;

    protected AbstractUndirectedNetworkConnections(Map<E, N> incidentEdgeMap) {
        this.incidentEdgeMap = checkNotNull(incidentEdgeMap);
    }

    @Override
    public Set<N> predecessors() {
        return adjacentNodes();
    }

    @Override
    public Set<N> successors() {
        return adjacentNodes();
    }

    @Override
    public Set<E> incidentEdges() {
        return Collections.unmodifiableSet(incidentEdgeMap.keySet());
    }

    @Override
    public Set<E> inEdges() {
        return incidentEdges();
    }

    @Override
    public Set<E> outEdges() {
        return incidentEdges();
    }

    @Override
    public N oppositeNode(Object edge) {
        return checkNotNull(incidentEdgeMap.get(edge));
    }

    @Override
    public N removeInEdge(Object edge, boolean isSelfLoop) {
        if (!isSelfLoop) {
            return removeOutEdge(edge);
        }
        return null;
    }

    @Override
    public N removeOutEdge(Object edge) {
        N previousNode = incidentEdgeMap.remove(edge);
        return checkNotNull(previousNode);
    }

    @Override
    public void addInEdge(E edge, N node, boolean isSelfLoop) {
        if (!isSelfLoop) {
            addOutEdge(edge, node);
        }
    }

    @Override
    public void addOutEdge(E edge, N node) {
        N previousNode = incidentEdgeMap.put(edge, node);
        checkState(previousNode == null);
    }
}
